Future internal combustion engines of motor vehicles, operating on the basis of jet-directed combustion methods, for example, have lower waste-heat losses due to better engine efficiency. In particular following a cold start, the engine heat is then often insufficient to heat up the passenger cabin. For this reason, the introduction of heat exchangers is taken into consideration, in which the exhaust gas of the engine heats the cooling water of the motor vehicle. In a warm engine, the heat exchanger is circumvented via a bypass with the aid of an actuating element in the exhaust branch.
A similar actuating element in the exhaust branch may also be useful for bypassing a NOx catalytic converter. In higher engine loads, in homogeneous operation, the exhaust gas will then not be conveyed via the NOx catalytic converter, but also via a bypass. This leads to lower thermal stress of the NOx catalytic converter, among others, and to a higher engine output due to the lower exhaust-gas counterpressure.
For reasons of emission and safety, the function of such actuating elements in the exhaust branch must be monitored. Monitoring may occur, for example, by a temperature sensor in the flow direction, downstream from the corresponding actuating element in the exhaust branch. Furthermore, it is conceivable to measure the position of the actuating element with the aid of a potentiometer. For this reason, a diagnosis of the function of the appropriate actuating element in the exhaust branch requires an additional sensor system.
Furthermore, internal combustion engines are known that include exhaust-gas recirculation via which exhaust gas from an exhaust branch is conveyed to an intake manifold of the internal combustion engine in an activated state.